Many industrial processes require oxygen-free nitrogen atmospheres. One such process, for example, is heat treating where the presence of oxygen for a prolonged period at high oven temperatures can deleteriously affect the parts being treated. Accordingly, heat treaters and the like have taken great pains to prevent the infiltration of air into their nitrogen environmental system. Typically, nitrogen is provided for such processes by nitrogen gas generators in which a combustible gas (e.g. natural gas) is burned with air to produce principally nitrogen, water and carbonaceous products (i.e., principally CO.sub.2 with small amounts of CO). The gas generator effluent is normally cooled, washed, dried and carbonaceous products removed (i.e., hereafter decarbonized) to yield the desired nitrogen atmosphere. Washing and cooling of the gas generator effluent is usually effected by passing it through a gas-liquid contact device such as a counterflow packed bed, or spray chamber where it is contacted with water resulting in a lowering of its temperature and saturation thereof (i.e., about 80.degree. F. dew point). The drying and decarbonizing is thereafter effected by passing the gas through gas separators containing conventional molecular sieve (e.g., synthetic zeolites) and desiccant (e.g., activated alumina) adsorbent beds which trap the water and carbonaceous molecules while permitting the smaller nitrogen molecules to pass. The molecular sieves and desiccants, however, have a limited capacity, eventually become saturated with adsorbate and must be regenerated. Accordingly, and in order to ensure a continuous flow of the pure nitrogen to the treatment area (e.g., heat treating ovens), it is customary to provide at least two of the gas separators, plumbed in parallel such that one of the separators can be purifying the nitrogen (i.e., adsorption mode) while the other is being regenerated (i.e., desorption mode). Appropriate automatically controlled valves are provided for alternately shifting back and forth between the separators so as to ensure the desired continuous flow. In order to ensure an oxygen-free nitrogen atmosphere for the ovens, regeneration of the separators has traditionally been accomplished by evacuating one of the separators (i.e., about 26 in. of Hg.) and flushing it with a portion (i.e., about 20%) of the pure nitrogen being generated from the other separator, then undergoing its adsorption mode. One such system is disclosed in Meyer U.S. Pat. No. 3,891,411. Significant savings in nitrogen generation and conservation of precious natural gas can be achieved if the amount of nitrogen used for regeneration could be reduced.
It is an object of the present invention to provide a molecular-sieve-purified, oxygen-free, nitrogen gas atmosphere generation system wherein only minimum quantities of the nitrogen gas generated is required for regeneration of the molecular sieve material. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows.